The present invention relates generally to osteosynthesis holding systems, such as those used for stabilization of the spinal column. In particular, a locking mechanism for securing a bone screw to a clamping element of an osteosynthesis holding system is provided. A removal device is provided for removing the bone screw, as a greater axial force is required to overcome the locking mechanism than is needed to engage the locking mechanism. A corresponding method for revision (removal) of the bone screw from the locking mechanism is also provided.
It is well known that in osteosynthesis holding systems in general, and in those systems used for stabilization of the spinal column in particular, a loosening of the bone screw which secures the clamping element to the bone segment occurs. When the bone screw becomes loose, the bone screw may move in an axial direction (i.e. a backing out of the screw may occur). This axial movement may result in a loosening of the entire system, as well as injury to the patient by the protruding screw. For example, injury of blood vessels and nerves in the cervical spine and esophagus are common.
Several alternatives exist for securing the bone screw to the bone plate or clamping element. For example, attachment or locking screws or expansion elements may be used to secure the bone screw in place.
It would be advantageous to provide a locking mechanism for a bone screw where no additional securing elements are necessary. It would be further advantageous to provide a locking mechanism where no active locking of the bone screw is needed. It would be still further advantageous if the connection formed by the locking mechanism is reversible, to provide for explantation (removal) of the bone screw. In addition, it would be advantageous if the locking mechanism allows for a pre-stressing of the bone screw between the clamping element and the bone segment after the locking element is engaged.
The methods and apparatus of the present invention provide the foregoing and other advantages.